Microscope



Aug. 27, 1968 MCLACHLAN, JR 3,398,634

MICROSCOPE Filed Aug. 27, 1964 4 Sheets-Sheet 1 g- D. MLACHLAN,'JR I3,398,634

MICROSCOPE Filed Aug. 27, 1964 4 Sheets-Sheet 2 I I v 1 lNViETOR. mil?1968 D. MCLACHLAN, JR 3,398,634

MICROSCOPE 4 Sheets-Sheet 5 Filed Aug. 27, 1964 m hm MzMVENTiR.

Aug. 27, 1968 MOLACHLAN, JR 4 MICROSCOPE Filed Aug. 27, 1964 4Sheets-Sheet 4 IN VENTOR.

United States Patent 3,398,634 MICROSCOPE Dan McLachlan, Jr., Columbus,Ohio, assignor to The Board of Trustees of the Ohio State University,Columbus, Ohio Filed Aug. 27, 1964, Ser. No. 392,479 14 Claims. (Cl.88--24) ABSTRACT OF THE DISCLOSURE A microscope optical system toincrease the useful depth of observation of an object to many times thefocal depth of the lens system being used. The object is illuminatedonly at its focal plane while the object is being scanned through thatplane. Thus, the out-of-focus parts of the object are always indarkness.

From the inception of microscopy dating back to the days of Kepler andDescartes, the problem of focal depth has plagued artisans in the use oflenses at high magnification. At least one prior art system made anattempt at improving the resolution in depth by scanning the samplethrough the focal plane in a direction parallel to the axis of the lens.With this procedure every part of the sample will sometime come intofocus; however, this encountered two other difficulties. The first isthat each of the out-of-focus points is magnified differentlyresultingin a background that is a record of conflicts. The background problemwas overcome by synchronously moving the object in such a manner as tomake the outof-focus and the in-focus points come into register. This,however, led to the second difiiculty in that the out-offocus imagesbecome cumulative during exposure to produce a milky background.

The present invention corrects the above difiiculties through a uniquemanner of illuminating the object in its focal plane together withscanning of the object to attain high resolution at great depths. Thatis, the principle of the microscope of the present invention is that theobject is illuminated only at the focal plane while the object is beingscanned through that plane. Thus, the out-of-focus parts of the objectare always in darkness.

It is accordingly a principal object of the present invention to providea new method and means of microscopy for increasing the focal depth ofobservation of an object.

A further object of the invention is to eliminate from being illuminatedthe background-or, out-of-focus part of the image, under observation.

Another object of the invention is to magnify only that part of theimage under observation that is in focus.

Still another object of the present invention is to provide a system ofmicroscopy for viewing extremely small objects of fine texture at highmagnification in focus for the complete depth of the object.

Other objects and features of the present invention will become apparentfrom the following detailed description when taken in conjunction withthe drawings in which:

FIGURE 1 is a schematic illustration of the principles of the deep focusmicroscope of the present invention;

FIGURE 2 is an imaginary object in cross-section;

FIGURE 2a is an imaginary object in cross-section with that portionilluminated shown in heavy lines;

FIGURE 2b is an imaginary object in cross-section that part which isvisible as viewed in the direction of the arrows;

FIGURE 2c that part which is both illuminated and unobstructed;

FIGURE 3 is a diagrammatic plan view of a preferred constructedembodiment; and

FIGURE 4 is a diagrammatic plan view of a preferred arrangement forilluminating the samples two sides.

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Referring now specifically to FIGURE 1, there is generally shown aschematic representation of a preferred embodiment comprising a sampleobject 10 for viewing, a lens 15 and a photographic plate 20. The object10, illustrated as having an irregular shape, is fixedly mounted on ablock 12 for positioning by means 13 relative to the lengs 15 and prism40. The lens 15 has a, diameter a and a focal length 1.

In the theory, the distance p from the lens 15 to the focal plane PP andthe distance g from the lens 15 to the plate 20 are related by theequation:

and the magnification is M =q p While the resolution on the focal planeFF is h A/Z sin U (3) Since the human eye can tolerate a circle ofconfusion of about 0.0125 cm. or 200 lines per inch under the bestconditions, there is a circle of confusion c which is all that amicroscope needs to attain at a given magnification M.

and this value c is also related to the angle U measured from theoptical axis to the periphery of the lens 15 and to an importantquantity D the optical focal depth. Since c/D =a/2p then we have anequation for the tolerated focal depth D D,=.025 p/aM If a sample wereinfinitely thin, the sample could be placed on the FP plane of FIGURE 1,and the ultimate results predicted by Equation 3 could be attained.However, for all practical samples, the depth of the sample, heretofore,had to be kept equal to or less than D expressed in Equation 5. Inactual practice, in metallurgy this is achieved by polishing thespecimens (an frac tography and other problems that are difiicult tostudy); in biology and histology, the sample is sliced thin such as by amicrotome; in the study of suspensoids, such as blood, the liquid isplaced between two glass plates and pressed; the mineralogist, at greatcost, grinds the speci mens until they are thin; and so on. But notechnique prior to the present invention has made it possible to takemicro-photographs of insects, bacteria, extremely small crystals; woventextiles, broken surfaces of metals, or such small objects of finetexture at high magnification in focus for the complete depth of theobject.

In the upper part of FIGURE 1, again referring thereto, there is shownthat part of the system that includes a light source 25, a lightobturator 31 having a slit 30, a lens 35 and a mirror-prism 40. Inoperation, the light from the slit is passed as a thin zone of light tothe mirror-prism 40. The light is reflected from the prism 40 to thesample object 10 in a direction perpendicular to the axis of the lens 35and Within the zone D representing the focal depth. If the entire lenssystem and apparatus is held fixed, that is, with the illuminated zonecoincident with the focal zone, while the sample is scanned through adistance (or depth) D mechanically, then we have a ratio of mechanicaldepth to focal depth of If, however, we have a slit depth D (seeFIGURE 1) that is greater than D.,, the resolution is not ultimate and Aconstructed preferred embodiment shown in plan view in FIGURE 3 includesapparatus that comprises a light source 25. The illuminating system isin principle the same as that for measuring differences in elevation onthe surfaces of samples of uneven contour. The light from source 25 ispassed through the slit 30 of the obturator 31. A satisfactory slit 30was produced by spraying flat-black paint on a microscope slide andcutting a line in the paint with a new razor blade. As measured by aBausch and Lomb Filar microscope Ramdsen eyepiece A 1.5 the two bestslits were relatively uniform in width and were 2.4 10- and 1.76 10- cm.wide. With an optical system that reduces the dimensions toone-twentieth, D values ranging down to 1.3 10- or 0.8 are obtained andare adequate for magnifications as high as 400' or 500.

The lenses 35 and 36 are conventional projection lenses and serve toproject the light on the mirror prism 40. The lens 35, similar to thelens 15, is of optical microscope quality due to the requirement of theaccuracy with which the slit width D must be impinged on the sample.

As indicated above, the light is reflected from the prism 40 to thesample object 10 in a direction perpendicular to the axis of theprojection lenses 35 and 36.

The traveling stage 12 supporting the object to be illuminated furtherincludes attachments for adjusting the relative position of the sample10 with the zone of illumination.

Adjustment of the sample 10 is affected in the vertical direction by therack and pinion arrangement 14 through the knob 15. Adjustment of thesample 10 is effected in the horizontal direction by the rack and pinion18 through the knob 19. Adjustment in a direction for moving the sampleparallel to the microscope axis is effected by the rack and pinion 16through the knob 17. To sweep the object back and forth through the zoneof illumination .(as described hereinafter) there is attached to knob 17an arm 21 by means of screws 21a and 21b. The arm 21 atits other end isattached by a thin wire belt 21 to a cluster of pulleys. The pulleys, inturn, are driven by a motor 22. The rate at which the object is sweptthrough the zone of illumination is, of course, related to the size ofthe pulleys 23 and the speed of the motor 22. Specifically, the pinion16b on the rack 16a of'the elevator has a one-fourth inch diameter sothat when the microscope is tilted to its horizontal position, thesample object 10 moves 0.0055 centimeter per degree of rotation of thegnarled knob. The knob 17 is attached to an arm 21 having an adjustablelength from two inches to four inches, permitting the sample 10 to movefrom 0.000055 centimeter per centimeter of motion of the end of the armto 0.00022 centimeter per centimeter. The motion of the arm 21 isactuated by a motor 22 running one revolution per minute with a wire 24over a cluster of pulleys 23 of a size ranging from /2, A, and V inch indiameter. This arrangement facilitates scanning the sample at variablerates from 0.00165 to 0.08 centimeter per second smoothly so that amicrophotograph can be taken in one sweep. Other mechanical means andarrangements for scanning the specimen is within the scope of theinvention.

The microscope tube 50 supporting the lens arrangement for viewing theilluminated object is focused by movement of the knob 52. This, in turn,positions the microscope tube in a direction parallel to its axis.

The eyepiece lens 15 directs the illuminated image through the darkbellows 60 to the utility means or photographic film 20. If a projectionscreen were substituted for the film 20, the bellows would, of course,be eliminlated.

Table 1 (at end hereof) shows the useful magnifications which might bedesired in the first column labeled M fellowed in columns 2, 3, 4, and 5by F focal length, NA the numerical aperture which is sin U and a/Zp,

the tangent of U. M is ,th power of the eyepiece and BL thebellows-length. Under these chosen conditions, the depth of focus D ascomputed from Equation6 is shown in column 8. The depth of mechanicalscan D shown in column 9 is computed in centimeters on the grounds thatwe wish the depth of view to be equal to the width of the field andthatmagnification will bring this width to 5 inches on a 4 x 5"photographic film In order to demonstrate the working principles of themicroscope, a piece of dendritic bismuth about two and one-half inchessquare and having block-like recesses in it about one-half inch deep wasmounted 45 to the axis of a 50 mm. lens and at a distance of 55 mm. Aphotograph of this material was taken at a magnification of about twowhile it was being uniformly illuminated by parallel light streaming inat right angles to the axis of the lens. The bright points on the sampleproduce circles of increasing diameter as the distance from opti mumfocus increases, so that the circles of confusion can almost be measuredwith a ruler. A slit of thickness D of the three millimeters wasdirected upon that portion of the sample that was in focus and at rightangles again to the axis of the lens. It'was noted that the outof-focusareas were in total darkness and thus not recorded, while the areas mostnearly in focus were relatively well resolved. By reducing the slitdepth D the illumination to about one millimeter before scanning throughD of about 40 millimeters, a great improvement in results was noticed.

The image viewed with the microscope of the invention is analogous tothat viewed by a helicopter pilot of a mountain terrain by moonlight.FIGURE 2 shows a cross-section of an imagined mountain rangeincorporating a dome D in a conventional terrain A and a plateau sectionB. FIGURE 2b shows the directions of the moons rays and the heavy linesdepict the only parts not left in darkness by shadows. FIGURE 20 showsby arrows the pilots lines of sight and the heavy lines depict the onlyparts of the mountains not obstructed from view by other parts. (Inorder to make this illustration fuly analogous to the present situation,the lines of sight are perpendicular to the moons rays.) Sincevisibility depends upon both illumination and non-obstruction, there isleft only the heavily lined portions shown in FIGURE 2d which the pilotcan possibly expect to see.

It is observed that in the plateau section B of FIGURE 2, only the topscan be seen. This is what was actually found with the dendritic bismuthtests mentioned above, since this dendrite happened to grow in a formclosely resembling a pueblo vilage and only the roofs could bephotographed. The dome D in FIGURE 2 is more representative of theminute objects that may be viewed with the microscope of the invention.This su ests that the orientation of the object is important. I

In the illustrations of FIGURES 1 and 2, the illumination is from onlyone direction; however, samples may be illuminated from more than onedirection by suitably placing small mirrors 70 and 71 on the stage 12 inan arrangement as shown in FIGURE 4. The mirrors are oriented so as toreflect the light across and within the focal zone. A light guardprevents illumination directly from the source.

In viewing transparent objects, like small quartz crystals or clear,synthetic fibers, it was noted that light entering the object is pipedto all parts of the object emerging most strongly at ends, edges, andcorners, thus producing illumination that is out of focus. To overcomethis reradiation, the objects should first be aerodized or mirrorfinished to make their surfaces opaque.

' 6 It is apparent that the scanning motion through the where U is theangle'of the periphery of said lens from its depth D need notnecessarily be parallel to the axis optical axi of the lens 35. Thedirection of movement may be at 5 A microscope as t fo th i laim 4wherein a almost any angle or even a non-straight line. It has beentolerable circle f confusion C i i the order of found, however, thatthese motions produce distortions 5 in the image but without impairingresolution. c=() 0125 M A further modification of this system of theinvention may include two or more arrangements suitably posirelated tothe focal depth D in accordance with tioned in order that stereographicpictures may be taken to give the illusion of depths. c/D =a/ 2p Aninteresting fact is that since all parts of the object are equaldistances from the lens while being phofor a tolerated focal depth Dtographed, this method gives isometric pictures, not perspectivepictures. o'=- P r Although the method and the bulk of discussion areillustrated with radiation in the vissible region of the A mlcrqscqpe asSet forth In clalm 4 W a spectrum, it is applicable to infrared,ultraviolet, electron means of adlustlng the focal length of SaidWorkplece (mirror or reflection), and ion bombardment microscopescomprises moving Said workpiece through a depth DM or the use of anyform of radiation where scattering which is a ratio of depth of movementto the focal depth. and focusing of radiation is involved. 7. Amicroscope as set forth in claim 4 wherein said TABLE 1.WORKING DATAFinal Lens diam- Magnlfica- Power of Focal Numerical eter+twice Power ofBellows Depth of Depth of Resolution Ratio of9to8 tlon Objective LengthAperture dpslzjaelcge Eyepiece length focus I scan MT (M.) (F, mm.) (NA)(a/2p) (Me) J (DOX Oc J (DM, cm.) 0 0 cm-) (DM/Dn) 10 2 48 0. 0s 0. 0s 510 1, 560 1. 27 31 31. 4 3.5 30 0. 09 0. 0e 10 7 556 0. 51 23 91.7 50 525 0.14 0 14 10 10 173 0. 25 13 141 100 10 16 0.30 0 31 10 10 40. 5 0.13s 325 200 10 16 0.30 0 31 20 10 20.2 0.06 s 297 300 20 3 0.60 0 75 207.5 5.5 0.04 4 730 400 20 8 0. 60 0. 75 20 10 4. 1 0. 03 4 732 500 20 30.60 0 75 20 12.5 3.3 0.02 4 605 What is claimed is: means of adjustingthe focal length of said workpiece 1. A microscope comprising: a lightsource, means 35 comprises means for scanning said workpiece through afor confining the illumination from said source, a condensdepth D whichis a ratio of depth of movement to the ing lens for projecting saidconfined illumination, a mirror focal depth. prism for reflecting saidillumination in a direction per- 8. A microscope as set forth in claim 1further compendicular to the axis of said condensing lens and withinprising two or more light sources and means for illumia given zone,utility means, a lens for projecting light renating said workpiece frommore than one direction.

fiected from a workpiece to said utility means, and means 9. Amicroscope as set forth in claim 1 further comfor adjusting the focallength of said projected light wherep i g means f adjusting the relativedirection of i by said zone of illumination is confined to the focalzone workpiece with respect to said focal zone.

of said workpiece. 10. A microscope as set forth in claim 1 wherein said2. A microscope as set forth in claim 1 wherein the light source,condensing lens, and mirror prism are duplidistance p from said lprojecting light f om aid workcated and alternately positioned toprovide stereographic piece, to the focal plane FP of said workpiece,said lens image reflection.

having a focal length 1, and wherein the distance q from 11. Amicroscope as set forth in claim 1' wherein said said lens to saidutility means are related by the equation ili y means is a Camera formaking Pictures Of Said 1 1 1 workpiece.

12. A microscope as set forth in claim 1 wherein said f P 9 utilitymeans is a projection screen for projecting said 3. microscope as setforth in claim 1 wherein the light image from aid workpiece. distance pfrom said lens, projecting light from said work- 13. A microscopecomprising: a radiation source P to the focal Plane FP of saidworkpiece, said lens means for confining the radiation from said source,a conevmg a focallength f, an wherein the distance q from densing lensfor projecting said confined radiation, a said lens to said utilitymeans are related by the equation mirror prism for reflecting saidradiation in a direction 1 1 1 perpendicular to the axis of saidcondensing lens and 5 wil liltl a giigentzgnfe, utility irllfans, alensd for1 projecting ra la ion re ec e rom a w-or piece to sai uti itymeans, and the magmficatlon and means for adjusting the focal length ofsaid projection =q P whereby said zone of radiation is confined to thefocal 4. A microscope as set forth in claim 1 wherein the Zone of Saidworkpiecedistance p from said lens, projecting light from saidworkmicroscPPe as set forth in claim 13 wherein Said piece, to tha focalplam f Said workpiece, Said lens radlatlon source is of the classcomprising infrared, ultrahaving a focal length I, and wherein thedistance q fr violet, electron, mirror, electron reflection and ionbomsaid lens to said utility means are related by the equation bardment-1 1 1 References Cited =5 5 UNITED STATES PATENTS and the ifi ti is1,169,843 2/ 6 W 8824 Mzq/p 2,351,753 6/1944 Flint et al 88-24X whilethe resolution on the focal plane FF is NORTON ANSHER, PrimaryExaminerh=)\/2n sin U R. A. WINTERCORN, Assistant Examiner.

